The present invention relates to law enforcement technologies and security, and more particularly to methods and systems for determining the origin and direction of travel of supersonic projectiles based on shockwave-only information.
Systems and methods are known that can determine the general direction and trajectory of supersonic projectiles, such as bullets and artillery shells by measuring parameters associated with the shockwave generated by a projectile. One such system, described in U.S. Pat. No. 5,241,518 includes at least three spaced-apart sensors, with each sensor incorporating three acoustic transducers arranged in a plane. The sensors generate signals in response to the shockwave which are related to the azimuth and elevation angle to the origin of the shockwave. Shock-wave-only measurements are unable to determine the distance between the sensor(s) and the origin of the shockwave. Distance information is typically obtained from the muzzle flash or muzzle blast.
The azimuth and elevation angle of a shooter with reference to the sensor location are typically determined by measuring Time-of-Arrival (TOA) information of the shockwave at each sensor. Each of the sensors encounters the shockwave at a different time and generates a signal in response to the shockwave pressure. The signals from the various sensors are processed, and a direction (azimuth and elevation) from the sensor(s) to the origin of the shockwave and hence the trajectory of the projectile can be determined.
Conventional systems employ microphones, which can be relatively closely spaced (e.g., 1 meter apart) or widely dispersed (e.g., mounted on a vehicle or carried by soldiers on a battlefield), and measure shockwave pressure omni-directionally at their respective locations. One exemplary antenna includes a total of 7 omni-directional microphones, with 6 microphones distributed over the surface of a sphere (approx. diameter 1 m) and the seventh microphone located in the center of the sphere. An arrangement with less than 7 microphones can produce lobes in the spatial sensitivity pattern of the microphone array.
The relatively large antenna size and the large number of sensors can be a major disadvantage, for example, in vehicle-mounted systems. In addition, prior systems sense sound pressure and hence require special high-pass and low-pass filters for correctly differentiating between shockwave signals and ambient noise signals. Ambient noise signals can be as large or even larger than shockwave sound pressures. In addition, systems that omni-directionally measure sound pressure can generate ambiguous solutions in which the Time-of-Arrival of the shockwave at a given set of sensors is nearly identical for two mirror-symmetric shooter locations.
It would therefore be desirable to provide a system and method that is able to determine the trajectory of a supersonic projectile with a smaller number of sensors that occupy less space, and is also capable of differentiating between shockwave signals and ambient noise and eliminating the ambiguity in the determination of the shooter position.